Through the mid-1980s, the windows for most commercial buildings, such as offices, schools, hospitals, hotels, government buildings, residences and the like were single glazed. The use of double glazed insulating glass assemblies in such buildings generally occurred thereafter. The framing system for the single glazed assemblies was generally formed using aluminum tube. Typically, there were no thermal breaks or barriers. As a result, these buildings are not thermally efficient and have substantial heat and cooling losses through the windows. It is estimated that the area of such inefficient single glazed windows is at least two billion square feet world wide. In the United States, thousands of commercial buildings were erected during the building boom that began about thirty (30) years ago. Most of these buildings have single glazed windows.
There have been a series of approaches to correcting this problem. Probably the most costly approach is to rip out the existing glazing and replace it with insulating glass. Sometimes a new framing system is installed as well further increasing the cost of full replacements. The primary disadvantage of this approach, other than cost, is that it opens the building to the elements and prevents a tenant from occupying the space while this replacement process takes place. In addition, there is a disposal cost of the existing materials. There is also repair cost, including painting, of the existing openings. These drawbacks together with the loss of tenancy, makes such an approach an expensive operation.
There have also been attempts to create a double glazed insulating glass unit in the field using the existing outboard pane. To date these approaches have also provided unsatisfactory results. One drawback is that great exactness of size is required and the quality of the seal presents a failure issue. Further, the labor cost of manufacturing insulating glass as the field is very high.
In Europe, in the past number of years, a double glazed system has begun to find favor as a super energy saver. The system generally is installed in new buildings. Typically, the outboard lite is an insulating unit. Another single lite of glass is located some distance back into the building from the outboard lite (4″-5″), creating a flu wall effect between the lites. The air passing between the two lites is generally mechanically driven. The air inlet is from inside and the outlet is also back into the inside. The inboard lite is generally operable (hinged) so that the glass can be cleaned in the event of dirt or moisture. The system, however, is very expensive, roughly three times the price of a single glazed system. But, the comfort and energy savings are substantial and Europe's energy costs are generally higher than in the United States.